External electronic printed circuit cards are known in the art for providing electronic devices in which they are interfaced with additional stored memory and other electronic functionality. Printed circuit boards in these printed circuit cards typically contain memory chips and other electronic components which provide additional memory capabilities to the electronic device as desired. One such use for modern printed circuit cards is in the printer art wherein a modular printed circuit card provides additional "font" styles to the printer by interfacing the printed circuit card in a slot in the printer so that the printer can access the fonts in memory on the card when necessary. Thus, the printed circuit boards in printed circuit cards must properly function whenever the card is in use or else the printer will not print in the correct text format. In order for the electronic components on the printed circuit board to function properly and efficiently, the printed circuit board in the printed circuit card must be adequately grounded to earth.
If an adequate ground is not provided to the printed circuit board, various problems arise during operation of the card, and therefore during operation of the device in which the card is interfaced. It is thus generally desirable to increase the ground-to-signal ratio in a printed circuit card so as to improve the signal flow therethrough to improve the signal transmission performance of the card.
Apart from the obvious signal transmission problems encountered when printed circuit boards in printed circuit cards are not adequately grounded, when a poor ground connection is made the printed circuit card usually suffers from electromagnetic interference (EMI) problems, and the deleterious effects of electrostatic discharge (ESD) which occur when electronic components on the card arc to the card's housing or casing.
There have been many arrangements proposed in the art to provide a good ground path between the printed circuit board in the printed circuit card and earth. For example, U.S. Pat. No. 5,288,247, Kaufman, assigned to the same assignee as the present invention, proposes a ground referencing plane for a printed circuit board in a printed circuit card that provides a low impedance return path to increase the ground-to-signal ratio of the card. A conductive shroud further covers the card's housing and provides a ground reference plane via the top plate of the housing. The ground plane protects the printed circuit card from EMI or ESD since a mounting bracket electrically connects the ground plane of the printed circuit card to a ground plane on the printed circuit board such that ESD or EMI induced voltages are shunted electrically though the mounting bracket to the ground plane on the printed circuit board.
While the arrangement disclosed in the Kaufman patent is an excellent construction for reducing the effects of EMI or ESD, providing mounting-brackets to both hold a printed circuit board in a printed circuit card and to ground the printed circuit board can be costly. Furthermore, this arrangement does not consistently ensure that the ground contact between the printed circuit board and the housing is complete, and therefore a poor ground-to-signal ratio will sometimes be achieved.
Ground clips for grounding computer system boards have also been proposed in the art. See, for example, U.S. Pat. No. 5,138,529, Colton et al. The Colton et al. patent teaches a supportive grounding clip for mounting a computer system board to a conductive computer chassis. The clip includes a base member for providing a ground connection with the computer chassis, and flexible support members attached to opposite ends of the base member for mounting the supportive ground clip to the computer system board.
The supportive ground clip of the Colton et al. patent is rather large, and must be fitted through an elliptical opening in the base of the chassis to grasp the chassis so that the computer system board can be grounded to it. In this fashion, the clip provides support for the computer system board, as the board's weight tends to urge the board against the chassis. The clip of the Colton et al. patent is not adapted to provide protection against electromagnetic interference or electrostatic discharge, and further, can only function with the rather large computer motherboards typically found in personal computers. Furthermore, this clip possess a complicated shape in order to accommodate the weight-bearing requirements which the clip is meant to fulfill.
Prior printed circuit cards are therefore not consistently adequately grounded by the grounding arrangements which have heretofore been employed. There exists a long-felt need in the art for mechanisms to provide consistent ground contact points in printed circuit cards to protect the printed circuit cards from EMI and ESD problems, and to provide a high ground-to-signal ratio for the cards. These needs have not heretofore been fulfilled in the art.